###source: AskOxford: Types of World English
I cannot understand two things in the paragraph:
1) what is the difference of the English of Afrikaners and white South Africans? They speak the same language, don't they?
Just as the Dutch, German, French, etc. all speak forms of English influenced by their mother tongue, so too with the English that developed in South Africa.
Upon moving to a new land, immigrants tend to lose their mother tongue influence in the first generation of children but in SA, English was not the mother tongue.
"English is the first language of only about 10 per cent of the population, but the second language of many others."
It was a second language, considerably influenced by other tongues.
2) Can we consider it a question tag or is it a response of the other person (echo question)?
It's a real tag, but it seems to be a catch-all tag similar to 'right'.
You're British, right? Though I can't make claim to understanding it perfectly, it sounds like, "so the situation is ..., right?".
Student or Learner